Light olefins, defined herein as ethylene, propylene, butylene and mixtures thereof, serve as feeds for the production of numerous important chemicals and polymers. Typically, light olefins are produced by cracking petroleum feeds. Because of the limited supply of competitive petroleum feeds, the opportunities to produce low cost light olefins from petroleum feeds are limited. Efforts to develop light olefin production technologies based on alternative feeds have increased.
An important type of alternate feed for the production of light olefins is oxygenate, such as, for example, alcohols, particularly methanol and ethanol, dimethyl ether, methyl ethyl ether, diethyl ether, dimethyl carbonate, and methyl formate. Many of these oxygenates may be produced by fermentation, or from synthesis gas derived from natural gas, petroleum liquids, carbonaceous materials, including coal, recycled plastics, municipal wastes, or any organic material. Because of the wide variety of sources, alcohol, alcohol derivatives, and other oxygenates have promise as an economical, non-petroleum source for light olefin production.
The catalysts used to promote the conversion of oxygenates to olefins are molecular sieve catalysts. Because ethylene and propylene are the most sought after products of such a reaction, research has focused on what catalysts are most selective to ethylene and/or propylene, and on methods for increasing the life and selectivity of the catalysts to ethylene and/or propylene.
The conversion of oxygenates to olefins generates and deposits carbonaceous material (coke) on the molecular sieve catalysts used to catalyze the conversion process. Over accumulation of these carbonaceous deposits will interfere with the catalyst's ability to promote the reaction. In order to avoid unwanted build-up of coke on the molecular sieve catalyst, the oxygenate to olefin process incorporates a second step comprising catalyst regeneration. During regeneration, the coke is removed from the catalyst by combustion with oxygen, which restores the catalytic activity of the catalyst. The regenerated catalyst then may be reused to catalyze the conversion of oxygenates to olefins.
Typically, oxygenate to olefin conversion and regeneration are conducted in two separate vessels. The coked catalyst is continuously withdrawn from the reaction vessel used for conversion to a regeneration vessel and regenerated catalyst is continuously withdrawn from the regeneration vessel and returned to the reaction vessel for conversion.
U.S. Pat. Nos. 6,023,005 and 6,166,282, both of which are incorporated herein by reference, disclose methods of producing ethylene and propylene by catalytic conversion of oxygenate in a fluidized bed reaction process which utilizes catalyst regeneration.
European Patent Application EP 1142639A1 discloses a process for adding an active source of a hydrogenation component dissolved in a non-aqueous solvent to a non-zeolitic molecular sieve catalytic particulate with little or no reduction in micropore volume to provide improved catalytic performance in hydrocracking, catalytic dewaxing, and isomerization of waxy feedstocks to provide improved lubricating oils. The hydrogenation component can be added to the catalyst in the form of a bis (beta-diketonato)metal (II) complex.
U.S. Pat. No. 4,350,614 to Schwartz teaches the introduction of a platinum group metal modified catalyst in a fluidized catalytic cracking (FCC) process in combination with increasing the oxygen input to the regeneration zone to burn carbon monoxide in the dense phase rather than in the dilute phase whereby reducing the temperature differential between the two phases, markedly reducing the temperature of the dilute phase while only moderately increasing the temperature of the dense phase.
U.S. Pat. No. 4,072,600 to Schwartz and U.S. Pat. No. 4,151,121 to Gladrow et al. provide additional disclosures pertaining to the use of platinum group metal in CO oxidation in FCC units. The catalyst containing platinum group metal used for carbon monoxide burning in FCC can be used in the presence of water and is highly active, such that an alumina support can be used.
In the regenerator of a methanol to olefin (MTO) process, in the absence of a CO combustion promoter metal, the oxidation of carbonaceous deposits to CO is fast relative to the conversion of CO to CO2. As a result of its slower rate, the conversion of CO to CO2 is not always complete within the lower dense phase of the fluid bed regenerator. When this reaction occurs in the upper dilute zone, the result is a temperature rise that can easily exceed 100° C. This phenomenon is frequently referred to as “afterburning.” Afterburning in the upper dilute phase of a regenerator can lead to excessive temperatures, causing damage or potential failure of the regenerator vessels or other components contained within the vessels.
Many metals are known to promote the oxidation of CO to CO2. An example is the use of Pt or Pd in the catalytic converter of an automobile. However, these same metals are known to catalyze reactions with light olefins and hydrogen, such as hydrogenation or hydrocracking reactions. Such reactions are undesirable in an oxygenates to olefins process, as they would cause a reduction in the yield of these light olefins.
Accordingly, it would be useful to provide a process for making olefins from oxygenate which avoids or reduces afterburning in the regenerator by employing a CO oxidation metal to completely convert the carbonaceous deposits to CO2 within the dense phase of the regenerator, without significantly reducing selectivity to primary olefins in the oxygenate to olefins reactor.